1. Field of the Invention
This invention relates to a method for fabricating a SOI device, and more particularly, to a method for fabricating a full depletion type SOI device capable of minimizing a change in threshold voltage of transistor according to a change in the thickness of semiconductor layer.
2. Description of the Related Art
With high performance of semiconductor devices, the semiconductor integration technology using SOI wafer having a stack structure of a buried oxide film sandwiched between a base substrate and a semiconductor layer instead of single crystal silicon wafer being comprised of a bulk silicon has been proposed. The semiconductor device integrated in SOI wafer (hereinafter, referred to SOI device) has advantages over the semiconductor integrated in single crystal silicon wafer in that it is capable of achieving the high speed by a low junction capacitance and reduction of latch-up by the complete device isolation.
The SOI device is classified into a full depletion type device and a part depletion type device according to the thickness of the semiconductor layer where the device is to be formed.
In the part depletion type SOI device, an error-operation is generated by a parasitic bipolar transistor and floating body effect such as a kink phenomenon since the body of a transistor is fully isolated by a field oxide film and a buried oxide film. As a result, an operation performance becomes unstable. However, in the full depletion type SOI device, a neutral layer is not present on boundary between a channel region and a source region since the channel region is fully depleted even though a gate voltage is 0V. As a result, the full depletion type SOI device is capable of preventing a floating body effect which is usually generated in the part depletion type SOI device.
Accordingly, more efforts are being made to develop the full depletion type SOI device than the part depletion type SOI device.
Despite the advantages of the full depletion type SOI devices, it is difficult to ensure a reliability because the threshold voltage of the transistor is considerably changed according to the change of the thickness of the semiconductor layer where a device is to be formed.
Therefore, it is an object of the invention to provide a method for fabricating a full depletion type SOI device capable of minimizing a change in threshold voltage of transistor according to the change in the thickness of a semiconductor layer.
There is provided to a method for fabricating a full depletion type SOI device comprising the steps of: preparing a SOI wafer having a stack structure consisting of a base substrate, a buried oxide film, and a semiconductor layer; forming a dummy gate on an active region of the semiconductor layer; forming source/drain regions on an active region of the semiconductor layer at both sides of the dummy gate; depositing an insulating film over the dummy gate and the semiconductor layer; polishing the insulating film using the dummy gate as a polishing stop layer; removing the dummy gate; etching a predetermined thickness of semiconductor layer exposed by the removal of the dummy gate; growing a delta doped silicon film and a silicon film doped in a low concentration on a remaining part of the semiconductor layer, the total thickness thereof being equal to that of the source/drain regions; and forming a gate having a gate oxide film on the silicon film doped in a low concentration.
The above objects and other features and advantages of the present invention will become more apparent in light of the following detailed description and the accompanying figures.